1. Field of the Invention
The present invention relates to a flame-retardant leather-like sheet substrate, a production method thereof, an artificial leather made of the flame-retardant leather-like sheet substrate, and chairs or vehicle seats faced with the artificial leather. Particularly, the present invention relates to a flame-retardant leather-like sheet substrate having a soft and high-quality feeling and excellent in the surface strength such as abrasion resistance and peel strength, a production method thereof and an artificial leather made of the flame-retardant leather-like sheet substrate. With the above properties, the flame-retardant leather-like sheet substrate and the artificial leather made thereof of the present invention are suitably used in various applications requiring high quality, flame retardance and high surface strength such as high abrasion resistance and high peel strength, for example, suitably used as the facing materials for vehicle seats and interior furniture such as cushion seats, sofas and chairs.
2. Description of the Prior Art
Artificial leathers have been conventionally used in various applications such as the facing materials for interiors, clothing, shoes, bags, gloves, and vehicle seats. Recently, of such applications, the facing materials for the vehicle seats such as railway coach seats, automotive seats, airplane seats and ship seats, and for the interior furniture such as cushion seats, sofas and chairs are strongly required to be made of flame-retardant artificial leathers for safety precautions.
The artificial leathers are roughly classified into two types—grained artificial leathers, i.e., leather-like sheet substrates having their surface grained by a wet or dry method, and suede artificial leathers, i.e., leather-like sheet substrates having their surface finished with naps. The artificial leathers of either types generally have a base leather-like sheet substrate comprising an entangled nonwoven fabric having its interspace between entangled fibers impregnated with an elastomeric polymer.
The leather-like sheet substrate or the artificial leather having its base made therefrom are generally made flame-retardant by (1) post-impregnating the leather-like sheet substrate or the grained or suede artificial leather with a flame retardant, (2) lining the back of the leather-like sheet substrate with a flame-retardant woven or knitted fabric, (3) producing the leather-like sheet substrate from fibers incorporated with flame-retardant fine particles, or (4) filling the interspace between entangled fibers of the entangled nonwoven fabric constituting the leather-like sheet substrate with an elastomeric polymer blended with a flame retardant.
In the method (1), when the leather-like sheet substrate is made of superfine fiber bundles, it is very difficult for the flame retardant to enter into the inside of the superfine fiber bundles even when having a fine particle size, leaving the greater part of the flame retardant outside the superfine fiber bundles or on the outer surface of the elastomeric polymer. As a result, the appearance of the artificial leather is spoiled by its surface grimed with the flame retardant, and a long-term flame-retardant effect is difficult to obtain because the flame retardant easily falls off. To prevent the flame retardant from falling off, proposed is to impregnate the leather-like sheet substrate or the artificial leather with a binder resin solution containing the flame retardant. However, it is still difficult by such a method to allow the flame retardant to permeate into the inside of the superfine fiber bundles, and the flame-retardant effect is rather significantly reduced because the surface of the flame retardant is covered with the binder resin. In addition, the flexibility of the leather-like sheet substrate or the artificial leather is spoiled by the impregnation of the binder resin and a sufficient nap-raising is not achieved.
In the method (2), the back of the leather-like sheet substrate or the artificial leather is generally lined with a flame-retardant sheet comprising a woven or knitted fabric containing a flame retardant such as phosphorus compounds and halogen compounds. However, the lining with the flame-retardant sheet is likely to spoil the soft and high-quality feeling that is characteristic of the artificial leather.
The fibers used in the method (3) are generally produced by melt-spinning a fiber-forming polymer such as polyamide and polyethylene incorporated with fine flame-retardant particles. However, the determination of the spinning temperature and the selection of the polymer and the flame retardant are restricted by the stability of the flame retardant and the polymer during the melt-spinning process. Since fiber break is likely to occur, the method is disadvantageous in view of productivity. In addition, since the fibers containing fine flame-retardant particles are significantly reduced in their fiber properties, the leather-like sheet substrate made of such fibers drastically lowers the abrasion-resistant strength of a resultant artificial leather. When such a leather-like sheet substrate is fabricated into a grained artificial leather, the peel strength of the grain surface is lowered, failing to obtain an artificial leather of practical value.
In the method (4), since the flame retardant is added only to the elastomeric polymer to fill the inside of nonwoven fabric without adding the flame retardant to the fibers to form the entangled nonwoven fabric for the leather-like sheet substrate, the flame-retardant effect is generally not sufficient. If the addition amount of the flame retardant to the elastomeric polymer is increased to enhance the flame-retardant effect, the feeling of the artificial leather becomes hard to lost the high-quality feeling.
To solve the above problems in the conventional technique, Japanese Patent Application Laid-Open No. 63-85185 proposes an artificial leather which is produced by the steps of forming a fiber substrate using fibers made of a flame-retardant polyester copolymerized with a phosphorus compound or a halogen compound; forming a microporous fiber substrate by impregnating the fiber substrate with a flame-retardant polyurethane solution containing a bromine-containing modified urethane compound, followed by wet-coagulation; and laminating the microporous fiber substrate with a particular polycarbonate polyurethane surface layer via a polycarbonate polyurethane adhesive layer containing antimony trioxide and a bromine-containing modified urethane compound. However, since a halogen-containing compound such as the bromine-containing modified urethane compound is used as the flame-retardant polyurethane to be impregnated into the fiber substrate and the adhesive polyurethane, the proposed artificial leather evolves harmful gas upon combustion to make it disadvantageous in view of environmental pollution. In the proposed artificial leather, the whole body of the fiber substrate for constituting the base microporous fiber substrate is made of the flame-retardant polyester fiber copolymerized with the phosphorus compound or the halogen compound, or made of the fiber containing the halogen flame retardant. These flame-retardant fibers are insufficient in the strength to result in a poor surface strength such as abrasion resistance and peel strength.
In these circumstances, the inventors have made study to solve the drawbacks in the conventional methods (1) to (4) and to develop a flame-retardant leather-like sheet substrate which is halogen-free, hard to cause environmental pollution, and excellent in safety and flame retardancy while retaining a good soft and high-quality feeling. As a result thereof, the inventors found a flame-retardant leather-like sheet substrate comprising an entangled nonwoven fabric having in its inside a polymer elastomer containing aluminum hydroxide, and have filed a patent application (Japanese Patent Application Laid-Open No. 2002-115183). The entangled nonwoven fabric is made of a flame-retardant superfine fiber having a single fiber fineness of 0.5 dtex or less which is produced from a flame-retardant copolyester copolymerized with an organic phosphorus compound. The flame-retardant leather-like sheet substrate found by the inventors has a soft and high-quality feeling as well as a good flame retardancy. In addition, it is excellent in the safety and the prevention of environmental pollution because of containing no harmful halogen. Therefore, the artificial leather, such as the grained artificial leather and the suede artificial leather, made from the flame-retardant leather-like sheet substrate is particularly suitable as the facing material for vehicle seats and interior furniture.
The inventors have continued the study on the basis of the above finding. As a result thereof, the inventors have found that the flame-retardant leather-like sheet substrate proposed in Japanese Patent Application Laid-Open No. 2002-115183 is desired to be further improved in its surface strength when intended to be used in applications requiring a high surface strength, for example, the use as the facing material for vehicle seats and interior furniture.
The production of fiber using a flame-retardant polyester copolymerized with a phosphorus-containing compound is conventionally known from other publications (for example, Japanese Patent Application Laid-Open Nos. 51-82392, 55-7888, and 2001-164423, and Japanese Patent Publication No. 55-41610), and a flame-retardant polyurethane having a phosphorus compound-derived structural unit introduced into its polyurethane molecule is also known (for example, Japanese Patent Application Laid-Open No. 9-194559). However, these patent documents are completely silent as to using the flame-retardant polyester fiber and the flame-retardant polyurethane in the production of the flame-retardant leather-like sheet substrate. Therefore, these patent documents describe or suggest nothing about providing the flame-retardant leather-like sheet substrate excellent in the flame retardancy as well as in the surface strength such as abrasion resistance and peel strength while having a soft and high-quality feeling.